ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 499 



Thu subgenus Faxonius is represented in our state by three species : ('. lirnusHs, 

 C. propiyiquus, and C. obscurus. Tlie firet is geographically, as well as niorplio- 

 logically, separated from the other two ; and here again it is the shape of the male 

 organs which serves as the chief distinguishing feature. Besides there are other 

 characters, such as the sliape and the spinosity of the carapace, which make it pos- 

 sible to recognize C. liraosus at a glance. N(j transitional forms being present, the 

 standing of C. limoms as a " good species " is beyond doubt. 



It is different with C. propinquus and ohscurn,<i, and the e.xtralimital form (.'. 

 sanborni. These three resemble each other very closely, and it is hard, indeed 

 impossible, without close examination to distinguish them. They also live under 

 similar ecological conditions, and their ranges together form a unit, so that it is evi- 

 dent that they are closely allied genetically. The differences of C. obacurus from the 

 other two forms are furnished by the " shoulder " of the male organ and the tubercles 

 of the annulus of the female, together with the complete lack of the median keel of 

 the rostrum. Other differences, such as .sculpture and spinosity of the chelipeds, 

 are of secondary value and not entirely reliable. But it must be emphasized that 

 within the established range of C. obscurus, from Fish Creek in the .southern part of 

 the Panhandle of West Virginia to the upper Alleghany and the Genessee Rivers 

 in INIcKean and Potter counties, and from Cheat River at the West \'irginia state- 

 line, to the upper Shenango River in Crawford County this species is remarkably 

 uniform in the character mentioned. No specimens have been found within this 

 area which show the slightest tendency toward C. jiropiiiqinis. 



Thus, with reference to this form, the postulate that a species should be sharply 

 and constantly separated from the coexisting allied forms is fulfilled (see Ortmann, 

 1896, p. 191) and accordingly I regard C. obscurus as a goorl species. 



As regards C. sanborni, matters seem to be slightly different. It agrees in the 

 shape of the sexual organs with V. pro]>in<juus, and differs only from the latter in 

 the lack of a rostral keel and some minor features in the armature of the chelipeds. 

 In the lack of a rostral keel it approaches V. obscurus, l)ut always may be distin- 

 guished by the shape of the sexual organs. Its relation to C /mipiuquus wmaws 

 doubtful. ]\Iy ol)servations do not cover the region in which possible transitions 

 might be expected (northern and western ( )hio), and thus I must leave this question 

 open, and I follow Faxon in regarding ('. sanhorui as a variety of C i/ropiuiiuus. 

 But it should be possible to settle this question by proper investigation, and I wouhl 

 not be astonished if it should be finally discovered that ('. siuthnrui actually is a 

 good specie-s, sharply and constantly separated from C. propiutpius. 



The subgenus Bartonius contains four species in Pennsylvania. One of them, 



